Search results for "Molar"

Dimesogenic liquid crystalline oligosiloxanes

1995

Abstract In this paper, the syntheses, phase properties and ferroelectric properties of new liquid crystalline oligosiloxane dimesogens are described. Smectic phases are dominant in this class of materials. Spontaneous polarizations are in the range of 10 to approximately 100 nCcm−2. The materials show interesting properties for display applications. Although offering higher mechanical stability than low molar mass materials, their switching is significantly faster (switching times in the range of some 10−5s) than is the case for similar side group polymers (typically some 10−3s). Therefore these new oligosiloxane derivatives may be ideal for building flexible displays. In addition, mixture…

Formation of micro- and nano-spheric particles (filter dust) during the preparation of cellulose acetate membranes

2003

Abstract Membranes were prepared from six samples of cellulose acetate (CA) differing in their average molecular weight (75–260 kg/mole) and molecular weight distribution using methyl acetate as solvent and 2-propanole as precipitant. The routes through the phase diagram and the evaporation times were varied in these experiments. Electron microscopy demonstrates that the amount of filter dust (CA particles deposited on the membrane surface) decreases as the fraction of low molecular weight material in the starting polymer becomes less. For low average molar mass of CA and moderate polymer concentrations in the casting solution the dust consists of individual spheres of relatively uniform si…

Morphology and Rheology of HDPE/LCP Blends Compatibilized by a Novel PE-g-LCP Copolymer

1999

A novel graft copolymer (PE-g-LCP) consisting of polyethylene (PE) backbones and liquid crystalline polymer (LCP) branches was synthesized via reactive blending of an acrylic acid-functionalized PE (Escor 5000 by Exxon) with a semiflexible LCP (SBH 1 : 1 : 2 by Eniricerche S.p.A.). The crude reactive blending product (COP) was shown by investigation of the fractions soluble in boiling toluene and xylene and of the residue to contain unreacted Escor and SBH, together with the graft copolymer forming the interphase. The compatibilizing activity of COP for PE/SBH blends, compared to that of pure Escor, was investigated using two PE grades. The COP addition into 80/20 PE/SBH blends caused a muc…

Star poly(2-ethyl-2-oxazoline)s-synthesis and thermosensitivity

2011

A series of star-shaped poly(2-ethyl-2-oxazoline)s was prepared by cationic polymerization. The polymerization was initiated by dipentaerythrityl hexakis(4-nitrobenzene sulfonate) and a tosylated hyperbranched polymer of glycidol. The polymerization proceeded in a controlled manner. The star structure of the products was determined by nuclear magnetic resonance. The molar mass distributions that were measured by gel permeation chromatography with multiangle laser light scattering were narrow, and the experimental values of the molar masses were close to those predicted. The very compact structure of the polymers obtained (compared with the linear counterparts) confirmed the star formation. …

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

2004

Abstract Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤ P n sc ≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d ∼( M n sc ) 0.476 . The contour length of the cylindrical brush polymers per main chain monomer unit, l m , was determined to slightly vary with side chain molar mass M n sc according to l m ∼( M n sc ) 0.059 . The resulting values are much less than the maximum exte…

Dominance of Chain Entanglement over Transient Sticking on Chain Dynamics in Hydrogen-Bonded Supramolecular Polymer Networks in the Melt

2018

The chain dynamics in supramolecular polymer networks is determined by the interplay of the kinetics of transient interchain association and relaxation of the network chains themselves. This interplay can be addressed by studying model supramolecular polymer networks in which the number of associative side groups and the molar mass of the covalently jointed backbone polymers are both varied systematically. To realize this idea, we use precursor chains with three different molar masses, which comes along with different extents of entanglement in the melt state. For each molar mass, the precursor polymers are functionalized with three different relative contents of associative side groups, gi…

Molecular characterization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide derivatives as potential self-assembling copolymers forming polymeric micelles

2003

A family of graft copolymers derivatives obtained from α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) have been studied as potential self-assembling macromolecules forming stable polymeric micelles at low critical micellar concentration. These polymers are obtained grafting on PHEA poly(ethylene glycol) (PEG) (Mw 5000 g/mol) (PHEA–PEG), hexadecylamine (PHEA–C16) or both moieties (PHEA–PEG–C16). The PHEA derivatives were characterised by a multi-angle light scattering (MALS) photometer on line to a size exclusion chromatography system in obtaining the molar mass distribution of the polymers. In addition, to investigate the capacity to form micellar aggregates in aqueous medium the MALS pho…

Hyperbranched aliphatic polyether polyols

2012

Hyperbranched polymers, dendritic macromolecules with branch-on-branch structures, have become an important polymer class since the early 1990s. They combine several advantages of the perfectly branched dendrimers with easy accessibility, typically in a one-step synthesis. Hyperbranched polyethers are a particularly interesting class of chemically stable and often biocompatible materials. Multifunctional hyperbranched polyethers with controllable molar mass and comparably low polydispersities can been prepared using hydroxyl-functional epoxides or oxetanes for polymerization via anionic and cationic polymerization mechanisms. Here, we review the progress in the preparation, characterization…

Loading of polymer nanocarriers: Factors, mechanisms and applications

2014

Abstract The progress in synthetic polymer chemistry has allowed the precise design of hybrid and multifunctional colloidal particles, which differ in type, size and shape, thus enhancing their possible applications as target-oriented carriers of low and high molar mass active species. This survey discusses the basic principles and factors, associated with the process of loading of polymeric nanoparticles. For the purpose of this review, the polymeric nano-carriers are divided into five most studied types: micelles, nanogels, capsules (incl. vesicles), dendrimers, and hybrid nanoparticles with porous cores. Factors influencing the loading are described and their importance discussed. An imp…

1984

The synthesis and phase behaviour of azo dye containing liquid crystalline side group copolymers are described. These Copolymers show the same electro-optical effects as low molar mass guest-host systems. Their macroscopic oriented nematic structure can be frozen in below the glass transition temperature resulting in a polymer film with dichroic properties. The behaviour of the copolymers (phase behaviour, surface and electric field orientation) can be improved via mixtures with low molar mass liquid crystals.